1. Field of the Invention
This invention relates to a device for conveying sheet material such as paper. More particularly, it is concerned with a sheet conveying device capable of effectively resuming conveyance of the sheet after operation has been stopped.
2. Description of Prior Arts
In recent years, reproduction apparatus and laser beam printers have become operated at higher and higher speeds, some of which are operable at as high a printing speed as 100 sheets per minute of A4-size paper.
In general, as the running speed of the reproduction machine increases, they become large in size with the consequent elongation of the distance between a paper feeding section and a receptacle for the print-out. As a result, there tends to occur the possibility that a number of sheets of paper remain in the apparatus when paper jamming takes place within the machine causing the conveyance of the sheets to stop. Also, when a door of the apparatus main body provided with a door-switch is opened during the machine operations, the sheet conveyance is also stopped for the sake of safety. On account of this, a number of sheets remain in the sheet conveying path of the reproduction apparatus as is the case with paper jamming.
When paper jamming takes place, an operator of the device is required to remove the paper from the jammed portion in the device, while keeping the minimum removal of paper from the conveying path other than the jammed portion, so that the machine operations may be resumed in the shortest possible length of time. The reason for this is that, even if the number of sheets output per unit time is large, when much time is taken for resuming machine operations, the high speed operating performance of the printing apparatus cannot be fully taken advantage of, whereby the through-put (processing capability) of the apparatus lowers. In general, the reproduction apparatus provides in it a high temperature section surrounding an image fixing device, or a section where the toner is transferred onto the printing sheet and is required to be conveyed to the image fixing device in a non-fixed state. Since the high temperature section and toner transfer section are liable to cause burning of fingers and palm, and staining of clothes on the part of a machine operator when he (or she) is going to remove the paper during stoppage of the apparatus, it is necessary to dispense with the need for the operator to remove the paper from the portion other than the jammed spot.
On the other hand, when the door switch is actuated, the conveying device usually stops instantaneously, on account of which interruption is brought about in the conveying operation which has been established in a certain definite sequence at the paper feeding section or resist-roller section in the conveying path. As a consequence of this, there is no warranty of continued sheet conveyance even when the door switch is immediately de-actuated, but there would rather be induced paper jamming. In order to avoid such situation, it has heretofore been required of the operator to remove paper from the conveying path, imposing on him additional work.